<?php
#
# Markdown Parser Interface
#

interface MarkdownInterface {

  #
  # Initialize the parser and return the result of its transform method.
  # This will work fine for derived classes too.
  #
  public static function defaultTransform($text);

  #
  # Main function. Performs some preprocessing on the input text
  # and pass it through the document gamut.
  #
  public function transform($text);

}

#
# Markdown Parser Class
#

class Markdown implements MarkdownInterface {

    ### Version ###

    const  MARKDOWNLIB_VERSION  =  "1.4.1";

    ### Simple Function Interface ###

    public static function defaultTransform($text) {
    #
    # Initialize the parser and return the result of its transform method.
    # This will work fine for derived classes too.
    #
        # Take parser class on which this function was called.
        $parser_class = 'Markdown';

        # try to take parser from the static parser list
        static $parser_list;
        $parser = &$parser_list[$parser_class];

        # create the parser it not already set
        if (!$parser)
            $parser = new $parser_class;

        # Transform text using parser.
        return $parser->transform($text);
    }

    ### Configuration Variables ###

    # Change to ">" for HTML output.
    public $empty_element_suffix = " />";
    public $tab_width = 4;
    
    # Change to `true` to disallow markup or entities.
    public $no_markup = false;
    public $no_entities = false;
    
    # Predefined urls and titles for reference links and images.
    public $predef_urls = array();
    public $predef_titles = array();

    # Optional filter function for URLs
    public $url_filter_func = null;


    ### Parser Implementation ###

    # Regex to match balanced [brackets].
    # Needed to insert a maximum bracked depth while converting to PHP.
    protected $nested_brackets_depth = 6;
    protected $nested_brackets_re;
    
    protected $nested_url_parenthesis_depth = 4;
    protected $nested_url_parenthesis_re;

    # Table of hash values for escaped characters:
    protected $escape_chars = '\`*_{}[]()>#+-.!';
    protected $escape_chars_re;


    public function __construct() {
    #
    # Constructor function. Initialize appropriate member variables.
    #
        $this->_initDetab();
        $this->prepareItalicsAndBold();
    
        $this->nested_brackets_re =
            str_repeat('(?>[^\[\]]+|\[', $this->nested_brackets_depth).
            str_repeat('\])*', $this->nested_brackets_depth);
    
        $this->nested_url_parenthesis_re =
            str_repeat('(?>[^()\s]+|\(', $this->nested_url_parenthesis_depth).
            str_repeat('(?>\)))*', $this->nested_url_parenthesis_depth);
        
        $this->escape_chars_re = '['.preg_quote($this->escape_chars).']';
        
        # Sort document, block, and span gamut in ascendent priority order.
        asort($this->document_gamut);
        asort($this->block_gamut);
        asort($this->span_gamut);
    }


    # Internal hashes used during transformation.
    protected $urls = array();
    protected $titles = array();
    protected $html_hashes = array();
    
    # Status flag to avoid invalid nesting.
    protected $in_anchor = false;
    
    
    protected function setup() {
    #
    # Called before the transformation process starts to setup parser 
    # states.
    #
        # Clear global hashes.
        $this->urls = $this->predef_urls;
        $this->titles = $this->predef_titles;
        $this->html_hashes = array();
        
        $this->in_anchor = false;
    }
    
    protected function teardown() {
    #
    # Called after the transformation process to clear any variable 
    # which may be taking up memory unnecessarly.
    #
        $this->urls = array();
        $this->titles = array();
        $this->html_hashes = array();
    }


    public function transform($text) {
    #
    # Main function. Performs some preprocessing on the input text
    # and pass it through the document gamut.
    #
        $this->setup();
    
        # Remove UTF-8 BOM and marker character in input, if present.
        $text = preg_replace('{^\xEF\xBB\xBF|\x1A}', '', $text);

        # Standardize line endings:
        #   DOS to Unix and Mac to Unix
        $text = preg_replace('{\r\n?}', "\n", $text);

        # Make sure $text ends with a couple of newlines:
        $text .= "\n\n";

        # Convert all tabs to spaces.
        $text = $this->detab($text);

        # Turn block-level HTML blocks into hash entries
        $text = $this->hashHTMLBlocks($text);

        # Strip any lines consisting only of spaces and tabs.
        # This makes subsequent regexen easier to write, because we can
        # match consecutive blank lines with /\n+/ instead of something
        # contorted like /[ ]*\n+/ .
        $text = preg_replace('/^[ ]+$/m', '', $text);

        # Run document gamut methods.
        foreach ($this->document_gamut as $method => $priority) {
            $text = $this->$method($text);
        }
        
        $this->teardown();

        return $text . "\n";
    }
    
    protected $document_gamut = array(
        # Strip link definitions, store in hashes.
        "stripLinkDefinitions" => 20,
        
        "runBasicBlockGamut"   => 30,
        );


    protected function stripLinkDefinitions($text) {
    #
    # Strips link definitions from text, stores the URLs and titles in
    # hash references.
    #
        $less_than_tab = $this->tab_width - 1;

        # Link defs are in the form: ^[id]: url "optional title"
        $text = preg_replace_callback('{
							^[ ]{0,'.$less_than_tab.'}\[(.+)\][ ]?:	# id = $1
							  [ ]*
							  \n?				# maybe *one* newline
							  [ ]*
							(?:
							  <(.+?)>			# url = $2
							|
							  (\S+?)			# url = $3
							)
							  [ ]*
							  \n?				# maybe one newline
							  [ ]*
							(?:
								(?<=\s)			# lookbehind for whitespace
								["(]
								(.*?)			# title = $4
								[")]
								[ ]*
							)?	# title is optional
							(?:\n+|\Z)
			}xm',
            array($this, '_stripLinkDefinitions_callback'),
            $text);

        return $text;
    }
    protected function _stripLinkDefinitions_callback($matches) {
        $link_id = strtolower($matches[1]);
        $url = $matches[2] == '' ? $matches[3] : $matches[2];
        $this->urls[$link_id] = $url;
        $this->titles[$link_id] = &$matches[4];

        return ''; # String that will replace the block
    }


    protected function hashHTMLBlocks($text) {
        if ($this->no_markup)  return $text;

        $less_than_tab = $this->tab_width - 1;

        # Hashify HTML blocks:
        # We only want to do this for block-level HTML tags, such as headers,
        # lists, and tables. That's because we still want to wrap <p>s around
        # "paragraphs" that are wrapped in non-block-level tags, such as anchors,
        # phrase emphasis, and spans. The list of tags we're looking for is
        # hard-coded:
        #
        # *  List "a" is made of tags which can be both inline or block-level.
        #    These will be treated block-level when the start tag is alone on 
        #    its line, otherwise they're not matched here and will be taken as 
        #    inline later.
        # *  List "b" is made of tags which are always block-level;
        #
        $block_tags_a_re = 'ins|del';
        $block_tags_b_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|'.
                           'script|noscript|style|form|fieldset|iframe|math|svg|'.
                           'article|section|nav|aside|hgroup|header|footer|'.
                           'figure';

        # Regular expression for the content of a block tag.
        $nested_tags_level = 4;
        $attr = '
			(?>				# optional tag attributes
			  \s			# starts with whitespace
			  (?>
				[^>"/]+		# text outside quotes
			  |
				/+(?!>)		# slash not followed by ">"
			  |
				"[^"]*"		# text inside double quotes (tolerate ">")
			  |
				\'[^\']*\'	# text inside single quotes (tolerate ">")
			  )*
			)?	
			';
        $content =
            str_repeat('
				(?>
				  [^<]+			# content without tag
				|
				  <\2			# nested opening tag
					'.$attr.'	# attributes
					(?>
					  />
					|
					  >', $nested_tags_level).    # end of opening tag
                      '.*?'.                    # last level nested tag content
            str_repeat('
					  </\2\s*>	# closing nested tag
					)
				  |				
					<(?!/\2\s*>	# other tags with a different name
				  )
				)*',
                $nested_tags_level);
        $content2 = str_replace('\2', '\3', $content);

        # First, look for nested blocks, e.g.:
        # 	<div>
        # 		<div>
        # 		tags for inner block must be indented.
        # 		</div>
        # 	</div>
        #
        # The outermost tags must start at the left margin for this to match, and
        # the inner nested divs must be indented.
        # We need to do this before the next, more liberal match, because the next
        # match will start at the first `<div>` and stop at the first `</div>`.
        $text = preg_replace_callback('{(?>
			(?>
				(?<=\n)			# Starting on its own line
				|				# or
				\A\n?			# the at beginning of the doc
			)
			(						# save in $1

			  # Match from `\n<tag>` to `</tag>\n`, handling nested tags 
			  # in between.
					
						[ ]{0,'.$less_than_tab.'}
						<('.$block_tags_b_re.')# start tag = $2
						'.$attr.'>			# attributes followed by > and \n
						'.$content.'		# content, support nesting
						</\2>				# the matching end tag
						[ ]*				# trailing spaces/tabs
						(?=\n+|\Z)	# followed by a newline or end of document

			| # Special version for tags of group a.

						[ ]{0,'.$less_than_tab.'}
						<('.$block_tags_a_re.')# start tag = $3
						'.$attr.'>[ ]*\n	# attributes followed by >
						'.$content2.'		# content, support nesting
						</\3>				# the matching end tag
						[ ]*				# trailing spaces/tabs
						(?=\n+|\Z)	# followed by a newline or end of document
					
			| # Special case just for <hr />. It was easier to make a special 
			  # case than to make the other regex more complicated.
			
						[ ]{0,'.$less_than_tab.'}
						<(hr)				# start tag = $2
						'.$attr.'			# attributes
						/?>					# the matching end tag
						[ ]*
						(?=\n{2,}|\Z)		# followed by a blank line or end of document
			
			| # Special case for standalone HTML comments:
			
					[ ]{0,'.$less_than_tab.'}
					(?s:
						<!-- .*? -->
					)
					[ ]*
					(?=\n{2,}|\Z)		# followed by a blank line or end of document
			
			| # PHP and ASP-style processor instructions (<? and <%)
			
					[ ]{0,'.$less_than_tab.'}
					(?s:
						<([?%])			# $2
						.*?
						\2>
					)
					[ ]*
					(?=\n{2,}|\Z)		# followed by a blank line or end of document
					
			)
			)}Sxmi',
            array($this, '_hashHTMLBlocks_callback'),
            $text);

        return $text;
    }
    protected function _hashHTMLBlocks_callback($matches) {
        $text = $matches[1];
        $key  = $this->hashBlock($text);

        return "\n\n$key\n\n";
    }
    
    
    protected function hashPart($text, $boundary = 'X') {
    #
    # Called whenever a tag must be hashed when a function insert an atomic 
    # element in the text stream. Passing $text to through this function gives
    # a unique text-token which will be reverted back when calling unhash.
    #
    # The $boundary argument specify what character should be used to surround
    # the token. By convension, "B" is used for block elements that needs not
    # to be wrapped into paragraph tags at the end, ":" is used for elements
    # that are word separators and "X" is used in the general case.
    #
        # Swap back any tag hash found in $text so we do not have to `unhash`
        # multiple times at the end.
        $text = $this->unhash($text);
        
        # Then hash the block.
        static $i = 0;
        $key = "$boundary\x1A" . ++$i . $boundary;
        $this->html_hashes[$key] = $text;

        return $key; # String that will replace the tag.
    }


    protected function hashBlock($text) {
    #
    # Shortcut function for hashPart with block-level boundaries.
    #
        return $this->hashPart($text, 'B');
    }


    protected $block_gamut = array(
    #
    # These are all the transformations that form block-level
    # tags like paragraphs, headers, and list items.
    #
        "doHeaders"         => 10,
        "doHorizontalRules" => 20,
        
        "doLists"           => 40,
        "doCodeBlocks"      => 50,
        "doBlockQuotes"     => 60,
        );

    protected function runBlockGamut($text) {
    #
    # Run block gamut tranformations.
    #
        # We need to escape raw HTML in Markdown source before doing anything 
        # else. This need to be done for each block, and not only at the 
        # begining in the Markdown function since hashed blocks can be part of
        # list items and could have been indented. Indented blocks would have 
        # been seen as a code block in a previous pass of hashHTMLBlocks.
        $text = $this->hashHTMLBlocks($text);
        
        return $this->runBasicBlockGamut($text);
    }
    
    protected function runBasicBlockGamut($text) {
    #
    # Run block gamut tranformations, without hashing HTML blocks. This is 
    # useful when HTML blocks are known to be already hashed, like in the first
    # whole-document pass.
    #
        foreach ($this->block_gamut as $method => $priority) {
            $text = $this->$method($text);
        }
        
        # Finally form paragraph and restore hashed blocks.
        $text = $this->formParagraphs($text);

        return $text;
    }
    
    
    protected function doHorizontalRules($text) {
        # Do Horizontal Rules:
        return preg_replace(
            '{
				^[ ]{0,3}	# Leading space
				([-*_])		# $1: First marker
				(?>			# Repeated marker group
					[ ]{0,2}	# Zero, one, or two spaces.
					\1			# Marker character
				){2,}		# Group repeated at least twice
				[ ]*		# Tailing spaces
				$			# End of line.
			}mx',
            "\n".$this->hashBlock("<hr$this->empty_element_suffix")."\n",
            $text);
    }


    protected $span_gamut = array(
    #
    # These are all the transformations that occur *within* block-level
    # tags like paragraphs, headers, and list items.
    #
        # Process character escapes, code spans, and inline HTML
        # in one shot.
        "parseSpan"           => -30,

        # Process anchor and image tags. Images must come first,
        # because ![foo][f] looks like an anchor.
        "doImages"            =>  10,
        "doAnchors"           =>  20,
        
        # Make links out of things like `<http://example.com/>`
        # Must come after doAnchors, because you can use < and >
        # delimiters in inline links like [this](<url>).
        "doAutoLinks"         =>  30,
        "encodeAmpsAndAngles" =>  40,

        "doItalicsAndBold"    =>  50,
        "doHardBreaks"        =>  60,
        );

    protected function runSpanGamut($text) {
    #
    # Run span gamut tranformations.
    #
        foreach ($this->span_gamut as $method => $priority) {
            $text = $this->$method($text);
        }

        return $text;
    }
    
    
    protected function doHardBreaks($text) {
        # Do hard breaks:
        return preg_replace_callback('/ {2,}\n/',
            array($this, '_doHardBreaks_callback'), $text);
    }
    protected function _doHardBreaks_callback($matches) {
        return $this->hashPart("<br$this->empty_element_suffix\n");
    }


    protected function doAnchors($text) {
    #
    # Turn Markdown link shortcuts into XHTML <a> tags.
    #
        if ($this->in_anchor) return $text;
        $this->in_anchor = true;
        
        #
        # First, handle reference-style links: [link text] [id]
        #
        $text = preg_replace_callback('{
			(					# wrap whole match in $1
			  \[
				('.$this->nested_brackets_re.')	# link text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]
			)
			}xs',
            array($this, '_doAnchors_reference_callback'), $text);

        #
        # Next, inline-style links: [link text](url "optional title")
        #
        $text = preg_replace_callback('{
			(				# wrap whole match in $1
			  \[
				('.$this->nested_brackets_re.')	# link text = $2
			  \]
			  \(			# literal paren
				[ \n]*
				(?:
					<(.+?)>	# href = $3
				|
					('.$this->nested_url_parenthesis_re.')	# href = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# Title = $7
				  \6		# matching quote
				  [ \n]*	# ignore any spaces/tabs between closing quote and )
				)?			# title is optional
			  \)
			)
			}xs',
            array($this, '_doAnchors_inline_callback'), $text);

        #
        # Last, handle reference-style shortcuts: [link text]
        # These must come last in case you've also got [link text][1]
        # or [link text](/foo)
        #
        $text = preg_replace_callback('{
			(					# wrap whole match in $1
			  \[
				([^\[\]]+)		# link text = $2; can\'t contain [ or ]
			  \]
			)
			}xs',
            array($this, '_doAnchors_reference_callback'), $text);

        $this->in_anchor = false;

        return $text;
    }
    protected function _doAnchors_reference_callback($matches) {
        $whole_match =  $matches[1];
        $link_text   =  $matches[2];
        $link_id     = &$matches[3];

        if ($link_id == "") {
            # for shortcut links like [this][] or [this].
            $link_id = $link_text;
        }
        
        # lower-case and turn embedded newlines into spaces
        $link_id = strtolower($link_id);
        $link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

        if (isset($this->urls[$link_id])) {
            $url = $this->urls[$link_id];
            $url = $this->encodeURLAttribute($url);
            
            $result = "<a href=\"$url\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }
        
            $link_text = $this->runSpanGamut($link_text);
            $result .= ">$link_text</a>";
            $result = $this->hashPart($result);
        }
        else {
            $result = $whole_match;
        }

        return $result;
    }
    protected function _doAnchors_inline_callback($matches) {
        $whole_match    =  $matches[1];
        $link_text        =  $this->runSpanGamut($matches[2]);
        $url            =  $matches[3] == '' ? $matches[4] : $matches[3];
        $title            = &$matches[7];

        // if the URL was of the form <s p a c e s> it got caught by the HTML
        // tag parser and hashed. Need to reverse the process before using the URL.
        $unhashed = $this->unhash($url);
        if ($unhashed != $url)
            $url = preg_replace('/^<(.*)>$/', '\1', $unhashed);

        $url = $this->encodeURLAttribute($url);

        $result = "<a href=\"$url\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\"";
        }
        
        $link_text = $this->runSpanGamut($link_text);
        $result .= ">$link_text</a>";

        return $this->hashPart($result);
    }


    protected function doImages($text) {
    #
    # Turn Markdown image shortcuts into <img> tags.
    #
        #
        # First, handle reference-style labeled images: ![alt text][id]
        #
        $text = preg_replace_callback('{
			(				# wrap whole match in $1
			  !\[
				('.$this->nested_brackets_re.')		# alt text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]

			)
			}xs',
            array($this, '_doImages_reference_callback'), $text);

        #
        # Next, handle inline images:  ![alt text](url "optional title")
        # Don't forget: encode * and _
        #
        $text = preg_replace_callback('{
			(				# wrap whole match in $1
			  !\[
				('.$this->nested_brackets_re.')		# alt text = $2
			  \]
			  \s?			# One optional whitespace character
			  \(			# literal paren
				[ \n]*
				(?:
					<(\S*)>	# src url = $3
				|
					('.$this->nested_url_parenthesis_re.')	# src url = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# title = $7
				  \6		# matching quote
				  [ \n]*
				)?			# title is optional
			  \)
			)
			}xs',
            array($this, '_doImages_inline_callback'), $text);

        return $text;
    }
    protected function _doImages_reference_callback($matches) {
        $whole_match = $matches[1];
        $alt_text    = $matches[2];
        $link_id     = strtolower($matches[3]);

        if ($link_id == "") {
            $link_id = strtolower($alt_text); # for shortcut links like ![this][].
        }

        $alt_text = $this->encodeAttribute($alt_text);
        if (isset($this->urls[$link_id])) {
            $url = $this->encodeURLAttribute($this->urls[$link_id]);
            $result = "<img src=\"$url\" alt=\"$alt_text\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }
            $result .= $this->empty_element_suffix;
            $result = $this->hashPart($result);
        }
        else {
            # If there's no such link ID, leave intact:
            $result = $whole_match;
        }

        return $result;
    }
    protected function _doImages_inline_callback($matches) {
        $whole_match    = $matches[1];
        $alt_text        = $matches[2];
        $url            = $matches[3] == '' ? $matches[4] : $matches[3];
        $title            = &$matches[7];

        $alt_text = $this->encodeAttribute($alt_text);
        $url = $this->encodeURLAttribute($url);
        $result = "<img src=\"$url\" alt=\"$alt_text\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\""; # $title already quoted
        }
        $result .= $this->empty_element_suffix;

        return $this->hashPart($result);
    }


    protected function doHeaders($text) {
        # Setext-style headers:
        #	  Header 1
        #	  ========
        #  
        #	  Header 2
        #	  --------
        #
        $text = preg_replace_callback('{ ^(.+?)[ ]*\n(=+|-+)[ ]*\n+ }mx',
            array($this, '_doHeaders_callback_setext'), $text);

        # atx-style headers:
        #	# Header 1
        #	## Header 2
        #	## Header 2 with closing hashes ##
        #	...
        #	###### Header 6
        #
        $text = preg_replace_callback('{
				^(\#{1,6})	# $1 = string of #\'s
				[ ]*
				(.+?)		# $2 = Header text
				[ ]*
				\#*			# optional closing #\'s (not counted)
				\n+
			}xm',
            array($this, '_doHeaders_callback_atx'), $text);

        return $text;
    }
    protected function _doHeaders_callback_setext($matches) {
        # Terrible hack to check we haven't found an empty list item.
        if ($matches[2] == '-' && preg_match('{^-(?: |$)}', $matches[1]))
            return $matches[0];
        
        $level = $matches[2]{0} == '=' ? 1 : 2;
        $block = "<h$level>".$this->runSpanGamut($matches[1])."</h$level>";

        return "\n" . $this->hashBlock($block) . "\n\n";
    }
    protected function _doHeaders_callback_atx($matches) {
        $level = strlen($matches[1]);
        $block = "<h$level>".$this->runSpanGamut($matches[2])."</h$level>";

        return "\n" . $this->hashBlock($block) . "\n\n";
    }


    protected function doLists($text) {
    #
    # Form HTML ordered (numbered) and unordered (bulleted) lists.
    #
        $less_than_tab = $this->tab_width - 1;

        # Re-usable patterns to match list item bullets and number markers:
        $marker_ul_re  = '[*+-]';
        $marker_ol_re  = '\d+[\.]';

        $markers_relist = array(
            $marker_ul_re => $marker_ol_re,
            $marker_ol_re => $marker_ul_re,
            );

        foreach ($markers_relist as $marker_re => $other_marker_re) {
            # Re-usable pattern to match any entirel ul or ol list:
            $whole_list_re = '
				(								# $1 = whole list
				  (								# $2
					([ ]{0,'.$less_than_tab.'})	# $3 = number of spaces
					('.$marker_re.')			# $4 = first list item marker
					[ ]+
				  )
				  (?s:.+?)
				  (								# $5
					  \z
					|
					  \n{2,}
					  (?=\S)
					  (?!						# Negative lookahead for another list item marker
						[ ]*
						'.$marker_re.'[ ]+
					  )
					|
					  (?=						# Lookahead for another kind of list
					    \n
						\3						# Must have the same indentation
						'.$other_marker_re.'[ ]+
					  )
				  )
				)
			'; // mx

            # We use a different prefix before nested lists than top-level lists.
            # See extended comment in _ProcessListItems().

            if ($this->list_level) {
                $text = preg_replace_callback('{
						^
						'.$whole_list_re.'
					}mx',
                    array($this, '_doLists_callback'), $text);
            }
            else {
                $text = preg_replace_callback('{
						(?:(?<=\n)\n|\A\n?) # Must eat the newline
						'.$whole_list_re.'
					}mx',
                    array($this, '_doLists_callback'), $text);
            }
        }

        return $text;
    }
    protected function _doLists_callback($matches) {
        # Re-usable patterns to match list item bullets and number markers:
        $marker_ul_re  = '[*+-]';
        $marker_ol_re  = '\d+[\.]';
        $marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";
        
        $list = $matches[1];
        $list_type = preg_match("/$marker_ul_re/", $matches[4]) ? "ul" : "ol";
        
        $marker_any_re = ($list_type == "ul" ? $marker_ul_re : $marker_ol_re);
        
        $list .= "\n";
        $result = $this->processListItems($list, $marker_any_re);
        
        $result = $this->hashBlock("<$list_type>\n" . $result . "</$list_type>");

        return "\n". $result ."\n\n";
    }

    protected $list_level = 0;

    protected function processListItems($list_str, $marker_any_re) {
    #
    #	Process the contents of a single ordered or unordered list, splitting it
    #	into individual list items.
    #
        # The $this->list_level global keeps track of when we're inside a list.
        # Each time we enter a list, we increment it; when we leave a list,
        # we decrement. If it's zero, we're not in a list anymore.
        #
        # We do this because when we're not inside a list, we want to treat
        # something like this:
        #
        #		I recommend upgrading to version
        #		8. Oops, now this line is treated
        #		as a sub-list.
        #
        # As a single paragraph, despite the fact that the second line starts
        # with a digit-period-space sequence.
        #
        # Whereas when we're inside a list (or sub-list), that line will be
        # treated as the start of a sub-list. What a kludge, huh? This is
        # an aspect of Markdown's syntax that's hard to parse perfectly
        # without resorting to mind-reading. Perhaps the solution is to
        # change the syntax rules such that sub-lists must start with a
        # starting cardinal number; e.g. "1." or "a.".

        $this->list_level++;

        # trim trailing blank lines:
        $list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

        $list_str = preg_replace_callback('{
			(\n)?							# leading line = $1
			(^[ ]*)							# leading whitespace = $2
			('.$marker_any_re.'				# list marker and space = $3
				(?:[ ]+|(?=\n))	# space only required if item is not empty
			)
			((?s:.*?))						# list item text   = $4
			(?:(\n+(?=\n))|\n)				# tailing blank line = $5
			(?= \n* (\z | \2 ('.$marker_any_re.') (?:[ ]+|(?=\n))))
			}xm',
            array($this, '_processListItems_callback'), $list_str);

        $this->list_level--;

        return $list_str;
    }
    protected function _processListItems_callback($matches) {
        $item = $matches[4];
        $leading_line = &$matches[1];
        $leading_space = &$matches[2];
        $marker_space = $matches[3];
        $tailing_blank_line = &$matches[5];

        if ($leading_line || $tailing_blank_line ||
            preg_match('/\n{2,}/', $item))
        {
            # Replace marker with the appropriate whitespace indentation
            $item = $leading_space . str_repeat(' ', strlen($marker_space)) . $item;
            $item = $this->runBlockGamut($this->outdent($item)."\n");
        }
        else {
            # Recursion for sub-lists:
            $item = $this->doLists($this->outdent($item));
            $item = preg_replace('/\n+$/', '', $item);
            $item = $this->runSpanGamut($item);
        }

        return "<li>" . $item . "</li>\n";
    }


    protected function doCodeBlocks($text) {
    #
    #	Process Markdown `<pre><code>` blocks.
    #
        $text = preg_replace_callback('{
				(?:\n\n|\A\n?)
				(	            # $1 = the code block -- one or more lines, starting with a space/tab
				  (?>
					[ ]{'.$this->tab_width.'}  # Lines must start with a tab or a tab-width of spaces
					.*\n+
				  )+
				)
				((?=^[ ]{0,'.$this->tab_width.'}\S)|\Z)	# Lookahead for non-space at line-start, or end of doc
			}xm',
            array($this, '_doCodeBlocks_callback'), $text);

        return $text;
    }
    protected function _doCodeBlocks_callback($matches) {
        $codeblock = $matches[1];

        $codeblock = $this->outdent($codeblock);
        $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);

        # trim leading newlines and trailing newlines
        $codeblock = preg_replace('/\A\n+|\n+\z/', '', $codeblock);

        $codeblock = "<pre><code>$codeblock\n</code></pre>";

        return "\n\n".$this->hashBlock($codeblock)."\n\n";
    }


    protected function makeCodeSpan($code) {
    #
    # Create a code span markup for $code. Called from handleSpanToken.
    #
        $code = htmlspecialchars(trim($code), ENT_NOQUOTES);

        return $this->hashPart("<code>$code</code>");
    }


    protected $em_relist = array(
        ''  => '(?:(?<!\*)\*(?!\*)|(?<!_)_(?!_))(?![\.,:;]?\s)',
        '*' => '(?<![\s*])\*(?!\*)',
        '_' => '(?<![\s_])_(?!_)',
        );
    protected $strong_relist = array(
        ''   => '(?:(?<!\*)\*\*(?!\*)|(?<!_)__(?!_))(?![\.,:;]?\s)',
        '**' => '(?<![\s*])\*\*(?!\*)',
        '__' => '(?<![\s_])__(?!_)',
        );
    protected $em_strong_relist = array(
        ''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<!_)___(?!_))(?![\.,:;]?\s)',
        '***' => '(?<![\s*])\*\*\*(?!\*)',
        '___' => '(?<![\s_])___(?!_)',
        );
    protected $em_strong_prepared_relist;
    
    protected function prepareItalicsAndBold() {
    #
    # Prepare regular expressions for searching emphasis tokens in any
    # context.
    #
        foreach ($this->em_relist as $em => $em_re) {
            foreach ($this->strong_relist as $strong => $strong_re) {
                # Construct list of allowed token expressions.
                $token_relist = array();
                if (isset($this->em_strong_relist["$em$strong"])) {
                    $token_relist[] = $this->em_strong_relist["$em$strong"];
                }
                $token_relist[] = $em_re;
                $token_relist[] = $strong_re;
                
                # Construct master expression from list.
                $token_re = '{('. implode('|', $token_relist) .')}';
                $this->em_strong_prepared_relist["$em$strong"] = $token_re;
            }
        }
    }
    
    protected function doItalicsAndBold($text) {
        $token_stack = array('');
        $text_stack = array('');
        $em = '';
        $strong = '';
        $tree_char_em = false;
        
        while (1) {
            #
            # Get prepared regular expression for seraching emphasis tokens
            # in current context.
            #
            $token_re = $this->em_strong_prepared_relist["$em$strong"];
            
            #
            # Each loop iteration search for the next emphasis token. 
            # Each token is then passed to handleSpanToken.
            #
            $parts = preg_split($token_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
            $text_stack[0] .= $parts[0];
            $token = &$parts[1];
            $text = &$parts[2];
            
            if (empty($token)) {
                # Reached end of text span: empty stack without emitting.
                # any more emphasis.
                while ($token_stack[0]) {
                    $text_stack[1] .= array_shift($token_stack);
                    $text_stack[0] .= array_shift($text_stack);
                }
                break;
            }
            
            $token_len = strlen($token);
            if ($tree_char_em) {
                # Reached closing marker while inside a three-char emphasis.
                if ($token_len == 3) {
                    # Three-char closing marker, close em and strong.
                    array_shift($token_stack);
                    $span = array_shift($text_stack);
                    $span = $this->runSpanGamut($span);
                    $span = "<strong><em>$span</em></strong>";
                    $text_stack[0] .= $this->hashPart($span);
                    $em = '';
                    $strong = '';
                } else {
                    # Other closing marker: close one em or strong and
                    # change current token state to match the other
                    $token_stack[0] = str_repeat($token{0}, 3 - $token_len);
                    $tag = $token_len == 2 ? "strong" : "em";
                    $span = $text_stack[0];
                    $span = $this->runSpanGamut($span);
                    $span = "<$tag>$span</$tag>";
                    $text_stack[0] = $this->hashPart($span);
                    $$tag = ''; # $$tag stands for $em or $strong
                }
                $tree_char_em = false;
            } elseif ($token_len == 3) {
                if ($em) {
                    # Reached closing marker for both em and strong.
                    # Closing strong marker:
                    for ($i = 0; $i < 2; ++$i) {
                        $shifted_token = array_shift($token_stack);
                        $tag = strlen($shifted_token) == 2 ? "strong" : "em";
                        $span = array_shift($text_stack);
                        $span = $this->runSpanGamut($span);
                        $span = "<$tag>$span</$tag>";
                        $text_stack[0] .= $this->hashPart($span);
                        $$tag = ''; # $$tag stands for $em or $strong
                    }
                } else {
                    # Reached opening three-char emphasis marker. Push on token 
                    # stack; will be handled by the special condition above.
                    $em = $token{0};
                    $strong = "$em$em";
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $tree_char_em = true;
                }
            } elseif ($token_len == 2) {
                if ($strong) {
                    # Unwind any dangling emphasis marker:
                    if (strlen($token_stack[0]) == 1) {
                        $text_stack[1] .= array_shift($token_stack);
                        $text_stack[0] .= array_shift($text_stack);
                    }
                    # Closing strong marker:
                    array_shift($token_stack);
                    $span = array_shift($text_stack);
                    $span = $this->runSpanGamut($span);
                    $span = "<strong>$span</strong>";
                    $text_stack[0] .= $this->hashPart($span);
                    $strong = '';
                } else {
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $strong = $token;
                }
            } else {
                # Here $token_len == 1
                if ($em) {
                    if (strlen($token_stack[0]) == 1) {
                        # Closing emphasis marker:
                        array_shift($token_stack);
                        $span = array_shift($text_stack);
                        $span = $this->runSpanGamut($span);
                        $span = "<em>$span</em>";
                        $text_stack[0] .= $this->hashPart($span);
                        $em = '';
                    } else {
                        $text_stack[0] .= $token;
                    }
                } else {
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $em = $token;
                }
            }
        }

        return $text_stack[0];
    }


    protected function doBlockQuotes($text) {
        $text = preg_replace_callback('/
			  (								# Wrap whole match in $1
				(?>
				  ^[ ]*>[ ]?			# ">" at the start of a line
					.+\n					# rest of the first line
				  (.+\n)*					# subsequent consecutive lines
				  \n*						# blanks
				)+
			  )
			/xm',
            array($this, '_doBlockQuotes_callback'), $text);

        return $text;
    }
    protected function _doBlockQuotes_callback($matches) {
        $bq = $matches[1];
        # trim one level of quoting - trim whitespace-only lines
        $bq = preg_replace('/^[ ]*>[ ]?|^[ ]+$/m', '', $bq);
        $bq = $this->runBlockGamut($bq);        # recurse

        $bq = preg_replace('/^/m', "  ", $bq);
        # These leading spaces cause problem with <pre> content, 
        # so we need to fix that:
        $bq = preg_replace_callback('{(\s*<pre>.+?</pre>)}sx',
            array($this, '_doBlockQuotes_callback2'), $bq);

        return "\n". $this->hashBlock("<blockquote>\n$bq\n</blockquote>")."\n\n";
    }
    protected function _doBlockQuotes_callback2($matches) {
        $pre = $matches[1];
        $pre = preg_replace('/^  /m', '', $pre);

        return $pre;
    }


    protected function formParagraphs($text) {
    #
    #	Params:
    #		$text - string to process with html <p> tags
    #
        # Strip leading and trailing lines:
        $text = preg_replace('/\A\n+|\n+\z/', '', $text);

        $grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

        #
        # Wrap <p> tags and unhashify HTML blocks
        #
        foreach ($grafs as $key => $value) {
            if (!preg_match('/^B\x1A[0-9]+B$/', $value)) {
                # Is a paragraph.
                $value = $this->runSpanGamut($value);
                $value = preg_replace('/^([ ]*)/', "<p>", $value);
                $value .= "</p>";
                $grafs[$key] = $this->unhash($value);
            }
            else {
                # Is a block.
                # Modify elements of @grafs in-place...
                $graf = $value;
                $block = $this->html_hashes[$graf];
                $graf = $block;
//				if (preg_match('{
//					\A
//					(							# $1 = <div> tag
//					  <div  \s+
//					  [^>]*
//					  \b
//					  markdown\s*=\s*  ([\'"])	#	$2 = attr quote char
//					  1
//					  \2
//					  [^>]*
//					  >
//					)
//					(							# $3 = contents
//					.*
//					)
//					(</div>)					# $4 = closing tag
//					\z
//					}xs', $block, $matches))
//				{
//					list(, $div_open, , $div_content, $div_close) = $matches;
//
//					# We can't call Markdown(), because that resets the hash;
//					# that initialization code should be pulled into its own sub, though.
//					$div_content = $this->hashHTMLBlocks($div_content);
//					
//					# Run document gamut methods on the content.
//					foreach ($this->document_gamut as $method => $priority) {
//						$div_content = $this->$method($div_content);
//					}
//
//					$div_open = preg_replace(
//						'{\smarkdown\s*=\s*([\'"]).+?\1}', '', $div_open);
//
//					$graf = $div_open . "\n" . $div_content . "\n" . $div_close;
//				}
                $grafs[$key] = $graf;
            }
        }

        return implode("\n\n", $grafs);
    }


    protected function encodeAttribute($text) {
    #
    # Encode text for a double-quoted HTML attribute. This function
    # is *not* suitable for attributes enclosed in single quotes.
    #
        $text = $this->encodeAmpsAndAngles($text);
        $text = str_replace('"', '&quot;', $text);

        return $text;
    }


    protected function encodeURLAttribute($url, &$text = null) {
    #
    # Encode text for a double-quoted HTML attribute containing a URL,
    # applying the URL filter if set. Also generates the textual
    # representation for the URL (removing mailto: or tel:) storing it in $text.
    # This function is *not* suitable for attributes enclosed in single quotes.
    #
        if ($this->url_filter_func)
            $url = call_user_func($this->url_filter_func, $url);

        if (preg_match('{^mailto:}i', $url))
            $url = $this->encodeEntityObfuscatedAttribute($url, $text, 7);
        elseif (preg_match('{^tel:}i', $url))
        {
            $url = $this->encodeAttribute($url);
            $text = substr($url, 4);
        }
        else
        {
            $url = $this->encodeAttribute($url);
            $text = $url;
        }

        return $url;
    }
    
    
    protected function encodeAmpsAndAngles($text) {
    #
    # Smart processing for ampersands and angle brackets that need to 
    # be encoded. Valid character entities are left alone unless the
    # no-entities mode is set.
    #
        if ($this->no_entities) {
            $text = str_replace('&', '&amp;', $text);
        } else {
            # Ampersand-encoding based entirely on Nat Irons's Amputator
            # MT plugin: <http://bumppo.net/projects/amputator/>
            $text = preg_replace('/&(?!#?[xX]?(?:[0-9a-fA-F]+|\w+);)/',
                                '&amp;', $text);
        }
        # Encode remaining <'s
        $text = str_replace('<', '&lt;', $text);

        return $text;
    }


    protected function doAutoLinks($text) {
        $text = preg_replace_callback('{<((https?|ftp|dict|tel):[^\'">\s]+)>}i',
            array($this, '_doAutoLinks_url_callback'), $text);

        # Email addresses: <address@domain.foo>
        $text = preg_replace_callback('{
			<
			(?:mailto:)?
			(
				(?:
					[-!#$%&\'*+/=?^_`.{|}~\w\x80-\xFF]+
				|
					".*?"
				)
				\@
				(?:
					[-a-z0-9\x80-\xFF]+(\.[-a-z0-9\x80-\xFF]+)*\.[a-z]+
				|
					\[[\d.a-fA-F:]+\]	# IPv4 & IPv6
				)
			)
			>
			}xi',
            array($this, '_doAutoLinks_email_callback'), $text);

        return $text;
    }
    protected function _doAutoLinks_url_callback($matches) {
        $url = $this->encodeURLAttribute($matches[1], $text);
        $link = "<a href=\"$url\">$text</a>";

        return $this->hashPart($link);
    }
    protected function _doAutoLinks_email_callback($matches) {
        $addr = $matches[1];
        $url = $this->encodeURLAttribute("mailto:$addr", $text);
        $link = "<a href=\"$url\">$text</a>";

        return $this->hashPart($link);
    }


    protected function encodeEntityObfuscatedAttribute($text, &$tail = null, $head_length = 0) {
    #
    #	Input: some text to obfuscate, e.g. "mailto:foo@example.com"
    #
    #	Output: the same text but with most characters encoded as either a
    #		decimal or hex entity, in the hopes of foiling most address
    #		harvesting spam bots. E.g.:
    #
    #        &#109;&#x61;&#105;&#x6c;&#116;&#x6f;&#58;&#x66;o&#111;
    #        &#x40;&#101;&#x78;&#97;&#x6d;&#112;&#x6c;&#101;&#46;&#x63;&#111;
    #        &#x6d;
    #
    #	Note: the additional output $tail is assigned the same value as the
    #	ouput, minus the number of characters specified by $head_length.
    #
    #	Based by a filter by Matthew Wickline, posted to BBEdit-Talk.
    #   With some optimizations by Milian Wolff. Forced encoding of HTML
    #	attribute special characters by Allan Odgaard.
    #
        if ($text == "") return $tail = "";

        $chars = preg_split('/(?<!^)(?!$)/', $text);
        $seed = (int) abs(crc32($text) / strlen($text)); # Deterministic seed.

        foreach ($chars as $key => $char) {
            $ord = ord($char);
            # Ignore non-ascii chars.
            if ($ord < 128) {
                $r = ($seed * (1 + $key)) % 100; # Pseudo-random function.
                # roughly 10% raw, 45% hex, 45% dec
                # '@' *must* be encoded. I insist.
                # '"' and '>' have to be encoded inside the attribute
                if ($r > 90 && strpos('@"&>', $char) === false) /* do nothing */;
                elseif ($r < 45) $chars[$key] = '&#x'.dechex($ord).';';
                else              $chars[$key] = '&#'.$ord.';';
            }
        }

        $text = implode('', $chars);
        $tail = $head_length ? implode('', array_slice($chars, $head_length)) : $text;

        return $text;
    }


    protected function parseSpan($str) {
    #
    # Take the string $str and parse it into tokens, hashing embeded HTML,
    # escaped characters and handling code spans.
    #
        $output = '';
        
        $span_re = '{
				(
					\\\\'.$this->escape_chars_re.'
				|
					(?<![`\\\\])
					`+						# code span marker
			'.($this->no_markup ? '' : '
				|
					<!--    .*?     -->		# comment
				|
					<\?.*?\?> | <%.*?%>		# processing instruction
				|
					<[!$]?[-a-zA-Z0-9:_]+	# regular tags
					(?>
						\s
						(?>[^"\'>]+|"[^"]*"|\'[^\']*\')*
					)?
					>
				|
					<[-a-zA-Z0-9:_]+\s*/> # xml-style empty tag
				|
					</[-a-zA-Z0-9:_]+\s*> # closing tag
			').'
				)
				}xs';

        while (1) {
            #
            # Each loop iteration seach for either the next tag, the next 
            # openning code span marker, or the next escaped character. 
            # Each token is then passed to handleSpanToken.
            #
            $parts = preg_split($span_re, $str, 2, PREG_SPLIT_DELIM_CAPTURE);
            
            # Create token from text preceding tag.
            if ($parts[0] != "") {
                $output .= $parts[0];
            }
            
            # Check if we reach the end.
            if (isset($parts[1])) {
                $output .= $this->handleSpanToken($parts[1], $parts[2]);
                $str = $parts[2];
            }
            else {
                break;
            }
        }
        
        return $output;
    }
    
    
    protected function handleSpanToken($token, &$str) {
    #
    # Handle $token provided by parseSpan by determining its nature and 
    # returning the corresponding value that should replace it.
    #
        switch ($token{0}) {
            case "\\":
                return $this->hashPart("&#". ord($token{1}). ";");
            case "`":
                # Search for end marker in remaining text.
                if (preg_match('/^(.*?[^`])'.preg_quote($token).'(?!`)(.*)$/sm',
                    $str, $matches))
                {
                    $str = $matches[2];
                    $codespan = $this->makeCodeSpan($matches[1]);

                    return $this->hashPart($codespan);
                }

                return $token; // return as text since no ending marker found.
            default:
                return $this->hashPart($token);
        }
    }


    protected function outdent($text) {
    #
    # Remove one level of line-leading tabs or spaces
    #
        return preg_replace('/^(\t|[ ]{1,'.$this->tab_width.'})/m', '', $text);
    }


    # String length function for detab. `_initDetab` will create a function to 
    # hanlde UTF-8 if the default function does not exist.
    protected $utf8_strlen = 'mb_strlen';
    
    protected function detab($text) {
    #
    # Replace tabs with the appropriate amount of space.
    #
        # For each line we separate the line in blocks delemited by
        # tab characters. Then we reconstruct every line by adding the 
        # appropriate number of space between each blocks.

        $text = preg_replace_callback('/^.*\t.*$/m',
            array($this, '_detab_callback'), $text);

        return $text;
    }
    protected function _detab_callback($matches) {
        $line = $matches[0];
        $strlen = $this->utf8_strlen; # strlen function for UTF-8.

        # Split in blocks.
        $blocks = explode("\t", $line);
        # Add each blocks to the line.
        $line = $blocks[0];
        unset($blocks[0]); # Do not add first block twice.
        foreach ($blocks as $block) {
            # Calculate amount of space, insert spaces, insert block.
            $amount = $this->tab_width -
                $strlen($line, 'UTF-8') % $this->tab_width;
            $line .= str_repeat(" ", $amount) . $block;
        }

        return $line;
    }
    protected function _initDetab() {
    #
    # Check for the availability of the function in the `utf8_strlen` property
    # (initially `mb_strlen`). If the function is not available, create a 
    # function that will loosely count the number of UTF-8 characters with a
    # regular expression.
    #
        if (function_exists($this->utf8_strlen)) return;
        $this->utf8_strlen = create_function('$text', 'return preg_match_all(
			"/[\\\\x00-\\\\xBF]|[\\\\xC0-\\\\xFF][\\\\x80-\\\\xBF]*/", 
			$text, $m);');
    }


    protected function unhash($text) {
    #
    # Swap back in all the tags hashed by _HashHTMLBlocks.
    #
        return preg_replace_callback('/(.)\x1A[0-9]+\1/',
            array($this, '_unhash_callback'), $text);
    }
    protected function _unhash_callback($matches) {
        return $this->html_hashes[$matches[0]];
    }

}


#
# Temporary Markdown Extra Parser Implementation Class
#
# NOTE: DON'T USE THIS CLASS
# Currently the implementation of of Extra resides here in this temporary class.
# This makes it easier to propagate the changes between the three different
# packaging styles of PHP Markdown. When this issue is resolved, this
# MarkdownExtra_TmpImpl class here will disappear and \Michelf\MarkdownExtra
# will contain the code. So please use \Michelf\MarkdownExtra and ignore this
# one.
#

abstract class _MarkdownExtra_TmpImpl extends Markdown {

    ### Configuration Variables ###

    # Prefix for footnote ids.
    public $fn_id_prefix = "";
    
    # Optional title attribute for footnote links and backlinks.
    public $fn_link_title = "";
    public $fn_backlink_title = "";
    
    # Optional class attribute for footnote links and backlinks.
    public $fn_link_class = "footnote-ref";
    public $fn_backlink_class = "footnote-backref";

    # Class name for table cell alignment (%% replaced left/center/right)
    # For instance: 'go-%%' becomes 'go-left' or 'go-right' or 'go-center'
    # If empty, the align attribute is used instead of a class name.
    public $table_align_class_tmpl = '';

    # Optional class prefix for fenced code block.
    public $code_class_prefix = "";
    # Class attribute for code blocks goes on the `code` tag;
    # setting this to true will put attributes on the `pre` tag instead.
    public $code_attr_on_pre = false;
    
    # Predefined abbreviations.
    public $predef_abbr = array();


    ### Parser Implementation ###

    public function __construct() {
    #
    # Constructor function. Initialize the parser object.
    #
        # Add extra escapable characters before parent constructor 
        # initialize the table.
        $this->escape_chars .= ':|';
        
        # Insert extra document, block, and span transformations. 
        # Parent constructor will do the sorting.
        $this->document_gamut += array(
            "doFencedCodeBlocks" => 5,
            "stripFootnotes"     => 15,
            "stripAbbreviations" => 25,
            "appendFootnotes"    => 50,
            );
        $this->block_gamut += array(
            "doFencedCodeBlocks" => 5,
            "doTables"           => 15,
            "doDefLists"         => 45,
            );
        $this->span_gamut += array(
            "doFootnotes"        => 5,
            "doAbbreviations"    => 70,
            );
        
        parent::__construct();
    }
    
    
    # Extra variables used during extra transformations.
    protected $footnotes = array();
    protected $footnotes_ordered = array();
    protected $footnotes_ref_count = array();
    protected $footnotes_numbers = array();
    protected $abbr_desciptions = array();
    protected $abbr_word_re = '';
    
    # Give the current footnote number.
    protected $footnote_counter = 1;
    
    
    protected function setup() {
    #
    # Setting up Extra-specific variables.
    #
        parent::setup();
        
        $this->footnotes = array();
        $this->footnotes_ordered = array();
        $this->footnotes_ref_count = array();
        $this->footnotes_numbers = array();
        $this->abbr_desciptions = array();
        $this->abbr_word_re = '';
        $this->footnote_counter = 1;
        
        foreach ($this->predef_abbr as $abbr_word => $abbr_desc) {
            if ($this->abbr_word_re)
                $this->abbr_word_re .= '|';
            $this->abbr_word_re .= preg_quote($abbr_word);
            $this->abbr_desciptions[$abbr_word] = trim($abbr_desc);
        }
    }
    
    protected function teardown() {
    #
    # Clearing Extra-specific variables.
    #
        $this->footnotes = array();
        $this->footnotes_ordered = array();
        $this->footnotes_ref_count = array();
        $this->footnotes_numbers = array();
        $this->abbr_desciptions = array();
        $this->abbr_word_re = '';
        
        parent::teardown();
    }
    
    
    ### Extra Attribute Parser ###

    # Expression to use to catch attributes (includes the braces)
    protected $id_class_attr_catch_re = '\{((?:[ ]*[#.a-z][-_:a-zA-Z0-9=]+){1,})[ ]*\}';
    # Expression to use when parsing in a context when no capture is desired
    protected $id_class_attr_nocatch_re = '\{(?:[ ]*[#.a-z][-_:a-zA-Z0-9=]+){1,}[ ]*\}';

    protected function doExtraAttributes($tag_name, $attr) {
    #
    # Parse attributes caught by the $this->id_class_attr_catch_re expression
    # and return the HTML-formatted list of attributes.
    #
    # Currently supported attributes are .class and #id.
    #
        if (empty($attr)) return "";
        
        # Split on components
        preg_match_all('/[#.a-z][-_:a-zA-Z0-9=]+/', $attr, $matches);
        $elements = $matches[0];

        # handle classes and ids (only first id taken into account)
        $classes = array();
        $attributes = array();
        $id = false;
        foreach ($elements as $element) {
            if ($element{0} == '.') {
                $classes[] = substr($element, 1);
            } elseif ($element{0} == '#') {
                if ($id === false) $id = substr($element, 1);
            } elseif (strpos($element, '=') > 0) {
                $parts = explode('=', $element, 2);
                $attributes[] = $parts[0] . '="' . $parts[1] . '"';
            }
        }

        # compose attributes as string
        $attr_str = "";
        if (!empty($id)) {
            $attr_str .= ' id="'.$id.'"';
        }
        if (!empty($classes)) {
            $attr_str .= ' class="'.implode(" ", $classes).'"';
        }
        if (!$this->no_markup && !empty($attributes)) {
            $attr_str .= ' '.implode(" ", $attributes);
        }

        return $attr_str;
    }


    protected function stripLinkDefinitions($text) {
    #
    # Strips link definitions from text, stores the URLs and titles in
    # hash references.
    #
        $less_than_tab = $this->tab_width - 1;

        # Link defs are in the form: ^[id]: url "optional title"
        $text = preg_replace_callback('{
							^[ ]{0,'.$less_than_tab.'}\[(.+)\][ ]?:	# id = $1
							  [ ]*
							  \n?				# maybe *one* newline
							  [ ]*
							(?:
							  <(.+?)>			# url = $2
							|
							  (\S+?)			# url = $3
							)
							  [ ]*
							  \n?				# maybe one newline
							  [ ]*
							(?:
								(?<=\s)			# lookbehind for whitespace
								["(]
								(.*?)			# title = $4
								[")]
								[ ]*
							)?	# title is optional
					(?:[ ]* '.$this->id_class_attr_catch_re.' )?  # $5 = extra id & class attr
							(?:\n+|\Z)
			}xm',
            array($this, '_stripLinkDefinitions_callback'),
            $text);

        return $text;
    }
    protected function _stripLinkDefinitions_callback($matches) {
        $link_id = strtolower($matches[1]);
        $url = $matches[2] == '' ? $matches[3] : $matches[2];
        $this->urls[$link_id] = $url;
        $this->titles[$link_id] = &$matches[4];
        $this->ref_attr[$link_id] = $this->doExtraAttributes("", $dummy = &$matches[5]);

        return ''; # String that will replace the block
    }


    ### HTML Block Parser ###

    # Tags that are always treated as block tags:
    protected $block_tags_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|form|fieldset|iframe|hr|legend|article|section|nav|aside|hgroup|header|footer|figcaption|figure';
                           
    # Tags treated as block tags only if the opening tag is alone on its line:
    protected $context_block_tags_re = 'script|noscript|style|ins|del|iframe|object|source|track|param|math|svg|canvas|audio|video';
    
    # Tags where markdown="1" default to span mode:
    protected $contain_span_tags_re = 'p|h[1-6]|li|dd|dt|td|th|legend|address';
    
    # Tags which must not have their contents modified, no matter where 
    # they appear:
    protected $clean_tags_re = 'script|style|math|svg';
    
    # Tags that do not need to be closed.
    protected $auto_close_tags_re = 'hr|img|param|source|track';
    

    protected function hashHTMLBlocks($text) {
    #
    # Hashify HTML Blocks and "clean tags".
    #
    # We only want to do this for block-level HTML tags, such as headers,
    # lists, and tables. That's because we still want to wrap <p>s around
    # "paragraphs" that are wrapped in non-block-level tags, such as anchors,
    # phrase emphasis, and spans. The list of tags we're looking for is
    # hard-coded.
    #
    # This works by calling _HashHTMLBlocks_InMarkdown, which then calls
    # _HashHTMLBlocks_InHTML when it encounter block tags. When the markdown="1" 
    # attribute is found within a tag, _HashHTMLBlocks_InHTML calls back
    #  _HashHTMLBlocks_InMarkdown to handle the Markdown syntax within the tag.
    # These two functions are calling each other. It's recursive!
    #
        if ($this->no_markup)  return $text;

        #
        # Call the HTML-in-Markdown hasher.
        #
        list($text) = $this->_hashHTMLBlocks_inMarkdown($text);
        
        return $text;
    }
    protected function _hashHTMLBlocks_inMarkdown($text, $indent = 0,
                                        $enclosing_tag_re = '', $span = false)
    {
    #
    # Parse markdown text, calling _HashHTMLBlocks_InHTML for block tags.
    #
    # *   $indent is the number of space to be ignored when checking for code 
    #     blocks. This is important because if we don't take the indent into 
    #     account, something like this (which looks right) won't work as expected:
    #
    #     <div>
    #         <div markdown="1">
    #         Hello World.  <-- Is this a Markdown code block or text?
    #         </div>  <-- Is this a Markdown code block or a real tag?
    #     <div>
    #
    #     If you don't like this, just don't indent the tag on which
    #     you apply the markdown="1" attribute.
    #
    # *   If $enclosing_tag_re is not empty, stops at the first unmatched closing 
    #     tag with that name. Nested tags supported.
    #
    # *   If $span is true, text inside must treated as span. So any double 
    #     newline will be replaced by a single newline so that it does not create 
    #     paragraphs.
    #
    # Returns an array of that form: ( processed text , remaining text )
    #
        if ($text === '') return array('', '');

        # Regex to check for the presense of newlines around a block tag.
        $newline_before_re = '/(?:^\n?|\n\n)*$/';
        $newline_after_re =
            '{
				^						# Start of text following the tag.
				(?>[ ]*<!--.*?-->)?		# Optional comment.
				[ ]*\n					# Must be followed by newline.
			}xs';
        
        # Regex to match any tag.
        $block_tag_re =
            '{
				(					# $2: Capture whole tag.
					</?					# Any opening or closing tag.
						(?>				# Tag name.
							'.$this->block_tags_re.'			|
							'.$this->context_block_tags_re.'	|
							'.$this->clean_tags_re.'        	|
							(?!\s)'.$enclosing_tag_re.'
						)
						(?:
							(?=[\s"\'/a-zA-Z0-9])	# Allowed characters after tag name.
							(?>
								".*?"		|	# Double quotes (can contain `>`)
								\'.*?\'   	|	# Single quotes (can contain `>`)
								.+?				# Anything but quotes and `>`.
							)*?
						)?
					>					# End of tag.
				|
					<!--    .*?     -->	# HTML Comment
				|
					<\?.*?\?> | <%.*?%>	# Processing instruction
				|
					<!\[CDATA\[.*?\]\]>	# CData Block
				'. (!$span ? ' # If not in span.
				|
					# Indented code block
					(?: ^[ ]*\n | ^ | \n[ ]*\n )
					[ ]{'.($indent + 4).'}[^\n]* \n
					(?>
						(?: [ ]{'.($indent + 4).'}[^\n]* | [ ]* ) \n
					)*
				|
					# Fenced code block marker
					(?<= ^ | \n )
					[ ]{0,'.($indent + 3).'}(?:~{3,}|`{3,})
									[ ]*
					(?:
					\.?[-_:a-zA-Z0-9]+ # standalone class name
					|
						'.$this->id_class_attr_nocatch_re.' # extra attributes
					)?
					[ ]*
					(?= \n )
				' : ''). ' # End (if not is span).
				|
					# Code span marker
					# Note, this regex needs to go after backtick fenced
					# code blocks but it should also be kept outside of the
					# "if not in span" condition adding backticks to the parser
					`+
				)
			}xs';

        
        $depth = 0;        # Current depth inside the tag tree.
        $parsed = "";    # Parsed text that will be returned.

        #
        # Loop through every tag until we find the closing tag of the parent
        # or loop until reaching the end of text if no parent tag specified.
        #
        do {
            #
            # Split the text using the first $tag_match pattern found.
            # Text before  pattern will be first in the array, text after
            # pattern will be at the end, and between will be any catches made 
            # by the pattern.
            #
            $parts = preg_split($block_tag_re, $text, 2,
                                PREG_SPLIT_DELIM_CAPTURE);
            
            # If in Markdown span mode, add a empty-string span-level hash 
            # after each newline to prevent triggering any block element.
            if ($span) {
                $void = $this->hashPart("", ':');
                $newline = "$void\n";
                $parts[0] = $void . str_replace("\n", $newline, $parts[0]) . $void;
            }
            
            $parsed .= $parts[0]; # Text before current tag.

            # If end of $text has been reached. Stop loop.
            if (count($parts) < 3) {
                $text = "";
                break;
            }
            
            $tag  = $parts[1]; # Tag to handle.
            $text = $parts[2]; # Remaining text after current tag.
            $tag_re = preg_quote($tag); # For use in a regular expression.

            #
            # Check for: Fenced code block marker.
            # Note: need to recheck the whole tag to disambiguate backtick
            # fences from code spans
            #
            if (preg_match('{^\n?([ ]{0,'.($indent + 3).'})(~{3,}|`{3,})[ ]*(?:\.?[-_:a-zA-Z0-9]+|'.$this->id_class_attr_nocatch_re.')?[ ]*\n?$}', $tag, $capture)) {
                # Fenced code block marker: find matching end marker.
                $fence_indent = strlen($capture[1]); # use captured indent in re
                $fence_re = $capture[2]; # use captured fence in re
                if (preg_match('{^(?>.*\n)*?[ ]{'.($fence_indent).'}'.$fence_re.'[ ]*(?:\n|$)}', $text,
                    $matches))
                {
                    # End marker found: pass text unchanged until marker.
                    $parsed .= $tag . $matches[0];
                    $text = substr($text, strlen($matches[0]));
                }
                else {
                    # No end marker: just skip it.
                    $parsed .= $tag;
                }
            }
            #
            # Check for: Indented code block.
            #
            elseif ($tag{0} == "\n" || $tag{0} == " ") {
                # Indented code block: pass it unchanged, will be handled 
                # later.
                $parsed .= $tag;
            }
            #
            # Check for: Code span marker
            # Note: need to check this after backtick fenced code blocks
            #
            elseif ($tag{0} == "`") {
                # Find corresponding end marker.
                $tag_re = preg_quote($tag);
                if (preg_match('{^(?>.+?|\n(?!\n))*?(?<!`)'.$tag_re.'(?!`)}',
                    $text, $matches))
                {
                    # End marker found: pass text unchanged until marker.
                    $parsed .= $tag . $matches[0];
                    $text = substr($text, strlen($matches[0]));
                }
                else {
                    # Unmatched marker: just skip it.
                    $parsed .= $tag;
                }
            }
            #
            # Check for: Opening Block level tag or
            #            Opening Context Block tag (like ins and del) 
            #               used as a block tag (tag is alone on it's line).
            #
            elseif (preg_match('{^<(?:'.$this->block_tags_re.')\b}', $tag) ||
                (preg_match('{^<(?:'.$this->context_block_tags_re.')\b}', $tag) &&
                    preg_match($newline_before_re, $parsed) &&
                    preg_match($newline_after_re, $text))
                )
            {
                # Need to parse tag and following text using the HTML parser.
                list($block_text, $text) =
                    $this->_hashHTMLBlocks_inHTML($tag . $text, "hashBlock", true);
                
                # Make sure it stays outside of any paragraph by adding newlines.
                $parsed .= "\n\n$block_text\n\n";
            }
            #
            # Check for: Clean tag (like script, math)
            #            HTML Comments, processing instructions.
            #
            elseif (preg_match('{^<(?:'.$this->clean_tags_re.')\b}', $tag) ||
                $tag{1} == '!' || $tag{1} == '?')
            {
                # Need to parse tag and following text using the HTML parser.
                # (don't check for markdown attribute)
                list($block_text, $text) =
                    $this->_hashHTMLBlocks_inHTML($tag . $text, "hashClean", false);
                
                $parsed .= $block_text;
            }
            #
            # Check for: Tag with same name as enclosing tag.
            #
            elseif ($enclosing_tag_re !== '' &&
                # Same name as enclosing tag.
                preg_match('{^</?(?:'.$enclosing_tag_re.')\b}', $tag))
            {
                #
                # Increase/decrease nested tag count.
                #
                if ($tag{1} == '/')                        $depth--;
                elseif ($tag{strlen($tag) - 2} != '/')    $depth++;

                if ($depth < 0) {
                    #
                    # Going out of parent element. Clean up and break so we
                    # return to the calling function.
                    #
                    $text = $tag . $text;
                    break;
                }
                
                $parsed .= $tag;
            }
            else {
                $parsed .= $tag;
            }
        } while ($depth >= 0);
        
        return array($parsed, $text);
    }
    protected function _hashHTMLBlocks_inHTML($text, $hash_method, $md_attr) {
    #
    # Parse HTML, calling _HashHTMLBlocks_InMarkdown for block tags.
    #
    # *   Calls $hash_method to convert any blocks.
    # *   Stops when the first opening tag closes.
    # *   $md_attr indicate if the use of the `markdown="1"` attribute is allowed.
    #     (it is not inside clean tags)
    #
    # Returns an array of that form: ( processed text , remaining text )
    #
        if ($text === '') return array('', '');
        
        # Regex to match `markdown` attribute inside of a tag.
        $markdown_attr_re = '
			{
				\s*			# Eat whitespace before the `markdown` attribute
				markdown
				\s*=\s*
				(?>
					(["\'])		# $1: quote delimiter		
					(.*?)		# $2: attribute value
					\1			# matching delimiter	
				|
					([^\s>]*)	# $3: unquoted attribute value
				)
				()				# $4: make $3 always defined (avoid warnings)
			}xs';
        
        # Regex to match any tag.
        $tag_re = '{
				(					# $2: Capture whole tag.
					</?					# Any opening or closing tag.
						[\w:$]+			# Tag name.
						(?:
							(?=[\s"\'/a-zA-Z0-9])	# Allowed characters after tag name.
							(?>
								".*?"		|	# Double quotes (can contain `>`)
								\'.*?\'   	|	# Single quotes (can contain `>`)
								.+?				# Anything but quotes and `>`.
							)*?
						)?
					>					# End of tag.
				|
					<!--    .*?     -->	# HTML Comment
				|
					<\?.*?\?> | <%.*?%>	# Processing instruction
				|
					<!\[CDATA\[.*?\]\]>	# CData Block
				)
			}xs';
        
        $original_text = $text;        # Save original text in case of faliure.

        $depth        = 0;    # Current depth inside the tag tree.
        $block_text    = "";    # Temporary text holder for current text.
        $parsed        = "";    # Parsed text that will be returned.

        #
        # Get the name of the starting tag.
        # (This pattern makes $base_tag_name_re safe without quoting.)
        #
        if (preg_match('/^<([\w:$]*)\b/', $text, $matches))
            $base_tag_name_re = $matches[1];

        #
        # Loop through every tag until we find the corresponding closing tag.
        #
        do {
            #
            # Split the text using the first $tag_match pattern found.
            # Text before  pattern will be first in the array, text after
            # pattern will be at the end, and between will be any catches made 
            # by the pattern.
            #
            $parts = preg_split($tag_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
            
            if (count($parts) < 3) {
                #
                # End of $text reached with unbalenced tag(s).
                # In that case, we return original text unchanged and pass the
                # first character as filtered to prevent an infinite loop in the 
                # parent function.
                #
                return array($original_text{0}, substr($original_text, 1));
            }
            
            $block_text .= $parts[0]; # Text before current tag.
            $tag         = $parts[1]; # Tag to handle.
            $text        = $parts[2]; # Remaining text after current tag.

            #
            # Check for: Auto-close tag (like <hr/>)
            #			 Comments and Processing Instructions.
            #
            if (preg_match('{^</?(?:'.$this->auto_close_tags_re.')\b}', $tag) ||
                $tag{1} == '!' || $tag{1} == '?')
            {
                # Just add the tag to the block as if it was text.
                $block_text .= $tag;
            }
            else {
                #
                # Increase/decrease nested tag count. Only do so if
                # the tag's name match base tag's.
                #
                if (preg_match('{^</?'.$base_tag_name_re.'\b}', $tag)) {
                    if ($tag{1} == '/')                        $depth--;
                    elseif ($tag{strlen($tag) - 2} != '/')    $depth++;
                }
                
                #
                # Check for `markdown="1"` attribute and handle it.
                #
                if ($md_attr &&
                    preg_match($markdown_attr_re, $tag, $attr_m) &&
                    preg_match('/^1|block|span$/', $attr_m[2] . $attr_m[3]))
                {
                    # Remove `markdown` attribute from opening tag.
                    $tag = preg_replace($markdown_attr_re, '', $tag);
                    
                    # Check if text inside this tag must be parsed in span mode.
                    $this->mode = $attr_m[2] . $attr_m[3];
                    $span_mode = $this->mode == 'span' || $this->mode != 'block' &&
                        preg_match('{^<(?:'.$this->contain_span_tags_re.')\b}', $tag);
                    
                    # Calculate indent before tag.
                    if (preg_match('/(?:^|\n)( *?)(?! ).*?$/', $block_text, $matches)) {
                        $strlen = $this->utf8_strlen;
                        $indent = $strlen($matches[1], 'UTF-8');
                    } else {
                        $indent = 0;
                    }
                    
                    # End preceding block with this tag.
                    $block_text .= $tag;
                    $parsed .= $this->$hash_method($block_text);
                    
                    # Get enclosing tag name for the ParseMarkdown function.
                    # (This pattern makes $tag_name_re safe without quoting.)
                    preg_match('/^<([\w:$]*)\b/', $tag, $matches);
                    $tag_name_re = $matches[1];
                    
                    # Parse the content using the HTML-in-Markdown parser.
                    list($block_text, $text)
                        = $this->_hashHTMLBlocks_inMarkdown($text, $indent,
                            $tag_name_re, $span_mode);
                    
                    # Outdent markdown text.
                    if ($indent > 0) {
                        $block_text = preg_replace("/^[ ]{1,$indent}/m", "",
                                                    $block_text);
                    }
                    
                    # Append tag content to parsed text.
                    if (!$span_mode)    $parsed .= "\n\n$block_text\n\n";
                    else                $parsed .= "$block_text";
                    
                    # Start over with a new block.
                    $block_text = "";
                }
                else $block_text .= $tag;
            }
            
        } while ($depth > 0);
        
        #
        # Hash last block text that wasn't processed inside the loop.
        #
        $parsed .= $this->$hash_method($block_text);
        
        return array($parsed, $text);
    }


    protected function hashClean($text) {
    #
    # Called whenever a tag must be hashed when a function inserts a "clean" tag
    # in $text, it passes through this function and is automaticaly escaped, 
    # blocking invalid nested overlap.
    #
        return $this->hashPart($text, 'C');
    }


    protected function doAnchors($text) {
    #
    # Turn Markdown link shortcuts into XHTML <a> tags.
    #
        if ($this->in_anchor) return $text;
        $this->in_anchor = true;
        
        #
        # First, handle reference-style links: [link text] [id]
        #
        $text = preg_replace_callback('{
			(					# wrap whole match in $1
			  \[
				('.$this->nested_brackets_re.')	# link text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]
			)
			}xs',
            array($this, '_doAnchors_reference_callback'), $text);

        #
        # Next, inline-style links: [link text](url "optional title")
        #
        $text = preg_replace_callback('{
			(				# wrap whole match in $1
			  \[
				('.$this->nested_brackets_re.')	# link text = $2
			  \]
			  \(			# literal paren
				[ \n]*
				(?:
					<(.+?)>	# href = $3
				|
					('.$this->nested_url_parenthesis_re.')	# href = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# Title = $7
				  \6		# matching quote
				  [ \n]*	# ignore any spaces/tabs between closing quote and )
				)?			# title is optional
			  \)
			  (?:[ ]? '.$this->id_class_attr_catch_re.' )?	 # $8 = id/class attributes
			)
			}xs',
            array($this, '_doAnchors_inline_callback'), $text);

        #
        # Last, handle reference-style shortcuts: [link text]
        # These must come last in case you've also got [link text][1]
        # or [link text](/foo)
        #
        $text = preg_replace_callback('{
			(					# wrap whole match in $1
			  \[
				([^\[\]]+)		# link text = $2; can\'t contain [ or ]
			  \]
			)
			}xs',
            array($this, '_doAnchors_reference_callback'), $text);

        $this->in_anchor = false;

        return $text;
    }
    protected function _doAnchors_reference_callback($matches) {
        $whole_match =  $matches[1];
        $link_text   =  $matches[2];
        $link_id     = &$matches[3];

        if ($link_id == "") {
            # for shortcut links like [this][] or [this].
            $link_id = $link_text;
        }
        
        # lower-case and turn embedded newlines into spaces
        $link_id = strtolower($link_id);
        $link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

        if (isset($this->urls[$link_id])) {
            $url = $this->urls[$link_id];
            $url = $this->encodeURLAttribute($url);
            
            $result = "<a href=\"$url\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }
            if (isset($this->ref_attr[$link_id]))
                $result .= $this->ref_attr[$link_id];
        
            $link_text = $this->runSpanGamut($link_text);
            $result .= ">$link_text</a>";
            $result = $this->hashPart($result);
        }
        else {
            $result = $whole_match;
        }

        return $result;
    }
    protected function _doAnchors_inline_callback($matches) {
        $whole_match    =  $matches[1];
        $link_text        =  $this->runSpanGamut($matches[2]);
        $url            =  $matches[3] == '' ? $matches[4] : $matches[3];
        $title            = &$matches[7];
        $attr  = $this->doExtraAttributes("a", $dummy = &$matches[8]);

        // if the URL was of the form <s p a c e s> it got caught by the HTML
        // tag parser and hashed. Need to reverse the process before using the URL.
        $unhashed = $this->unhash($url);
        if ($unhashed != $url)
            $url = preg_replace('/^<(.*)>$/', '\1', $unhashed);

        $url = $this->encodeURLAttribute($url);

        $result = "<a href=\"$url\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\"";
        }
        $result .= $attr;
        
        $link_text = $this->runSpanGamut($link_text);
        $result .= ">$link_text</a>";

        return $this->hashPart($result);
    }


    protected function doImages($text) {
    #
    # Turn Markdown image shortcuts into <img> tags.
    #
        #
        # First, handle reference-style labeled images: ![alt text][id]
        #
        $text = preg_replace_callback('{
			(				# wrap whole match in $1
			  !\[
				('.$this->nested_brackets_re.')		# alt text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]

			)
			}xs',
            array($this, '_doImages_reference_callback'), $text);

        #
        # Next, handle inline images:  ![alt text](url "optional title")
        # Don't forget: encode * and _
        #
        $text = preg_replace_callback('{
			(				# wrap whole match in $1
			  !\[
				('.$this->nested_brackets_re.')		# alt text = $2
			  \]
			  \s?			# One optional whitespace character
			  \(			# literal paren
				[ \n]*
				(?:
					<(\S*)>	# src url = $3
				|
					('.$this->nested_url_parenthesis_re.')	# src url = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# title = $7
				  \6		# matching quote
				  [ \n]*
				)?			# title is optional
			  \)
			  (?:[ ]? '.$this->id_class_attr_catch_re.' )?	 # $8 = id/class attributes
			)
			}xs',
            array($this, '_doImages_inline_callback'), $text);

        return $text;
    }
    protected function _doImages_reference_callback($matches) {
        $whole_match = $matches[1];
        $alt_text    = $matches[2];
        $link_id     = strtolower($matches[3]);

        if ($link_id == "") {
            $link_id = strtolower($alt_text); # for shortcut links like ![this][].
        }

        $alt_text = $this->encodeAttribute($alt_text);
        if (isset($this->urls[$link_id])) {
            $url = $this->encodeURLAttribute($this->urls[$link_id]);
            $result = "<img src=\"$url\" alt=\"$alt_text\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }
            if (isset($this->ref_attr[$link_id]))
                $result .= $this->ref_attr[$link_id];
            $result .= $this->empty_element_suffix;
            $result = $this->hashPart($result);
        }
        else {
            # If there's no such link ID, leave intact:
            $result = $whole_match;
        }

        return $result;
    }
    protected function _doImages_inline_callback($matches) {
        $whole_match    = $matches[1];
        $alt_text        = $matches[2];
        $url            = $matches[3] == '' ? $matches[4] : $matches[3];
        $title            = &$matches[7];
        $attr  = $this->doExtraAttributes("img", $dummy = &$matches[8]);

        $alt_text = $this->encodeAttribute($alt_text);
        $url = $this->encodeURLAttribute($url);
        $result = "<img src=\"$url\" alt=\"$alt_text\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\""; # $title already quoted
        }
        $result .= $attr;
        $result .= $this->empty_element_suffix;

        return $this->hashPart($result);
    }


    protected function doHeaders($text) {
    #
    # Redefined to add id and class attribute support.
    #
        # Setext-style headers:
        #	  Header 1  {#header1}
        #	  ========
        #  
        #	  Header 2  {#header2 .class1 .class2}
        #	  --------
        #
        $text = preg_replace_callback(
            '{
				(^.+?)								# $1: Header text
				(?:[ ]+ '.$this->id_class_attr_catch_re.' )?	 # $3 = id/class attributes
				[ ]*\n(=+|-+)[ ]*\n+				# $3: Header footer
			}mx',
            array($this, '_doHeaders_callback_setext'), $text);

        # atx-style headers:
        #	# Header 1        {#header1}
        #	## Header 2       {#header2}
        #	## Header 2 with closing hashes ##  {#header3.class1.class2}
        #	...
        #	###### Header 6   {.class2}
        #
        $text = preg_replace_callback('{
				^(\#{1,6})	# $1 = string of #\'s
				[ ]*
				(.+?)		# $2 = Header text
				[ ]*
				\#*			# optional closing #\'s (not counted)
				(?:[ ]+ '.$this->id_class_attr_catch_re.' )?	 # $3 = id/class attributes
				[ ]*
				\n+
			}xm',
            array($this, '_doHeaders_callback_atx'), $text);

        return $text;
    }
    protected function _doHeaders_callback_setext($matches) {
        if ($matches[3] == '-' && preg_match('{^- }', $matches[1]))
            return $matches[0];
        $level = $matches[3]{0} == '=' ? 1 : 2;
        $attr  = $this->doExtraAttributes("h$level", $dummy = &$matches[2]);
        $block = "<h$level$attr>".$this->runSpanGamut($matches[1])."</h$level>";

        return "\n" . $this->hashBlock($block) . "\n\n";
    }
    protected function _doHeaders_callback_atx($matches) {
        $level = strlen($matches[1]);
        $attr  = $this->doExtraAttributes("h$level", $dummy = &$matches[3]);
        $block = "<h$level$attr>".$this->runSpanGamut($matches[2])."</h$level>";

        return "\n" . $this->hashBlock($block) . "\n\n";
    }


    protected function doTables($text) {
    #
    # Form HTML tables.
    #
        $less_than_tab = $this->tab_width - 1;
        #
        # Find tables with leading pipe.
        #
        #	| Header 1 | Header 2
        #	| -------- | --------
        #	| Cell 1   | Cell 2
        #	| Cell 3   | Cell 4
        #
        $text = preg_replace_callback('
			{
				^							# Start of a line
				[ ]{0,'.$less_than_tab.'}	# Allowed whitespace.
				[|]							# Optional leading pipe (present)
				(.+) \n						# $1: Header row (at least one pipe)
				
				[ ]{0,'.$less_than_tab.'}	# Allowed whitespace.
				[|] ([ ]*[-:]+[-| :]*) \n	# $2: Header underline
				
				(							# $3: Cells
					(?>
						[ ]*				# Allowed whitespace.
						[|] .* \n			# Row content.
					)*
				)
				(?=\n|\Z)					# Stop at final double newline.
			}xm',
            array($this, '_doTable_leadingPipe_callback'), $text);
        
        #
        # Find tables without leading pipe.
        #
        #	Header 1 | Header 2
        #	-------- | --------
        #	Cell 1   | Cell 2
        #	Cell 3   | Cell 4
        #
        $text = preg_replace_callback('
			{
				^							# Start of a line
				[ ]{0,'.$less_than_tab.'}	# Allowed whitespace.
				(\S.*[|].*) \n				# $1: Header row (at least one pipe)
				
				[ ]{0,'.$less_than_tab.'}	# Allowed whitespace.
				([-:]+[ ]*[|][-| :]*) \n	# $2: Header underline
				
				(							# $3: Cells
					(?>
						.* [|] .* \n		# Row content
					)*
				)
				(?=\n|\Z)					# Stop at final double newline.
			}xm',
            array($this, '_DoTable_callback'), $text);

        return $text;
    }
    protected function _doTable_leadingPipe_callback($matches) {
        $head        = $matches[1];
        $underline    = $matches[2];
        $content    = $matches[3];
        
        # Remove leading pipe for each row.
        $content    = preg_replace('/^ *[|]/m', '', $content);
        
        return $this->_doTable_callback(array($matches[0], $head, $underline, $content));
    }
    protected function _doTable_makeAlignAttr($alignname)
    {
        if (empty($this->table_align_class_tmpl))
            return " align=\"$alignname\"";

        $classname = str_replace('%%', $alignname, $this->table_align_class_tmpl);

        return " class=\"$classname\"";
    }
    protected function _doTable_callback($matches) {
        $head        = $matches[1];
        $underline    = $matches[2];
        $content    = $matches[3];

        # Remove any tailing pipes for each line.
        $head        = preg_replace('/[|] *$/m', '', $head);
        $underline    = preg_replace('/[|] *$/m', '', $underline);
        $content    = preg_replace('/[|] *$/m', '', $content);
        
        # Reading alignement from header underline.
        $separators    = preg_split('/ *[|] */', $underline);
        foreach ($separators as $n => $s) {
            if (preg_match('/^ *-+: *$/', $s))
                $attr[$n] = $this->_doTable_makeAlignAttr('right');
            elseif (preg_match('/^ *:-+: *$/', $s))
                $attr[$n] = $this->_doTable_makeAlignAttr('center');
            elseif (preg_match('/^ *:-+ *$/', $s))
                $attr[$n] = $this->_doTable_makeAlignAttr('left');
            else
                $attr[$n] = '';
        }
        
        # Parsing span elements, including code spans, character escapes, 
        # and inline HTML tags, so that pipes inside those gets ignored.
        $head        = $this->parseSpan($head);
        $headers    = preg_split('/ *[|] */', $head);
        $col_count    = count($headers);
        $attr       = array_pad($attr, $col_count, '');
        
        # Write column headers.
        $text = "<table>\n";
        $text .= "<thead>\n";
        $text .= "<tr>\n";
        foreach ($headers as $n => $header)
            $text .= "  <th$attr[$n]>".$this->runSpanGamut(trim($header))."</th>\n";
        $text .= "</tr>\n";
        $text .= "</thead>\n";
        
        # Split content by row.
        $rows = explode("\n", trim($content, "\n"));
        
        $text .= "<tbody>\n";
        foreach ($rows as $row) {
            # Parsing span elements, including code spans, character escapes, 
            # and inline HTML tags, so that pipes inside those gets ignored.
            $row = $this->parseSpan($row);
            
            # Split row by cell.
            $row_cells = preg_split('/ *[|] */', $row, $col_count);
            $row_cells = array_pad($row_cells, $col_count, '');
            
            $text .= "<tr>\n";
            foreach ($row_cells as $n => $cell)
                $text .= "  <td$attr[$n]>".$this->runSpanGamut(trim($cell))."</td>\n";
            $text .= "</tr>\n";
        }
        $text .= "</tbody>\n";
        $text .= "</table>";
        
        return $this->hashBlock($text) . "\n";
    }

    
    protected function doDefLists($text) {
    #
    # Form HTML definition lists.
    #
        $less_than_tab = $this->tab_width - 1;

        # Re-usable pattern to match any entire dl list:
        $whole_list_re = '(?>
			(								# $1 = whole list
			  (								# $2
				[ ]{0,'.$less_than_tab.'}
				((?>.*\S.*\n)+)				# $3 = defined term
				\n?
				[ ]{0,'.$less_than_tab.'}:[ ]+ # colon starting definition
			  )
			  (?s:.+?)
			  (								# $4
				  \z
				|
				  \n{2,}
				  (?=\S)
				  (?!						# Negative lookahead for another term
					[ ]{0,'.$less_than_tab.'}
					(?: \S.*\n )+?			# defined term
					\n?
					[ ]{0,'.$less_than_tab.'}:[ ]+ # colon starting definition
				  )
				  (?!						# Negative lookahead for another definition
					[ ]{0,'.$less_than_tab.'}:[ ]+ # colon starting definition
				  )
			  )
			)
		)'; // mx

        $text = preg_replace_callback('{
				(?>\A\n?|(?<=\n\n))
				'.$whole_list_re.'
			}mx',
            array($this, '_doDefLists_callback'), $text);

        return $text;
    }
    protected function _doDefLists_callback($matches) {
        # Re-usable patterns to match list item bullets and number markers:
        $list = $matches[1];
        
        # Turn double returns into triple returns, so that we can make a
        # paragraph for the last item in a list, if necessary:
        $result = trim($this->processDefListItems($list));
        $result = "<dl>\n" . $result . "\n</dl>";

        return $this->hashBlock($result) . "\n\n";
    }


    protected function processDefListItems($list_str) {
    #
    #	Process the contents of a single definition list, splitting it
    #	into individual term and definition list items.
    #
        $less_than_tab = $this->tab_width - 1;
        
        # trim trailing blank lines:
        $list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

        # Process definition terms.
        $list_str = preg_replace_callback('{
			(?>\A\n?|\n\n+)					# leading line
			(								# definition terms = $1
				[ ]{0,'.$less_than_tab.'}	# leading whitespace
				(?!\:[ ]|[ ])				# negative lookahead for a definition
											#   mark (colon) or more whitespace.
				(?> \S.* \n)+?				# actual term (not whitespace).	
			)			
			(?=\n?[ ]{0,3}:[ ])				# lookahead for following line feed 
											#   with a definition mark.
			}xm',
            array($this, '_processDefListItems_callback_dt'), $list_str);

        # Process actual definitions.
        $list_str = preg_replace_callback('{
			\n(\n+)?						# leading line = $1
			(								# marker space = $2
				[ ]{0,'.$less_than_tab.'}	# whitespace before colon
				\:[ ]+						# definition mark (colon)
			)
			((?s:.+?))						# definition text = $3
			(?= \n+ 						# stop at next definition mark,
				(?:							# next term or end of text
					[ ]{0,'.$less_than_tab.'} \:[ ]	|
					<dt> | \z
				)						
			)					
			}xm',
            array($this, '_processDefListItems_callback_dd'), $list_str);

        return $list_str;
    }
    protected function _processDefListItems_callback_dt($matches) {
        $terms = explode("\n", trim($matches[1]));
        $text = '';
        foreach ($terms as $term) {
            $term = $this->runSpanGamut(trim($term));
            $text .= "\n<dt>" . $term . "</dt>";
        }

        return $text . "\n";
    }
    protected function _processDefListItems_callback_dd($matches) {
        $leading_line    = $matches[1];
        $marker_space    = $matches[2];
        $def            = $matches[3];

        if ($leading_line || preg_match('/\n{2,}/', $def)) {
            # Replace marker with the appropriate whitespace indentation
            $def = str_repeat(' ', strlen($marker_space)) . $def;
            $def = $this->runBlockGamut($this->outdent($def . "\n\n"));
            $def = "\n". $def ."\n";
        }
        else {
            $def = rtrim($def);
            $def = $this->runSpanGamut($this->outdent($def));
        }

        return "\n<dd>" . $def . "</dd>\n";
    }


    protected function doFencedCodeBlocks($text) {
    #
    # Adding the fenced code block syntax to regular Markdown:
    #
    # ~~~
    # Code block
    # ~~~
    #
        $less_than_tab = $this->tab_width;
        
        $text = preg_replace_callback('{
				(?:\n|\A)
				# 1: Opening marker
				(
					(?:~{3,}|`{3,}) # 3 or more tildes/backticks.
				)
				[ ]*
				(?:
					\.?([-_:a-zA-Z0-9]+) # 2: standalone class name
				|
					'.$this->id_class_attr_catch_re.' # 3: Extra attributes
				)?
				[ ]* \n # Whitespace and newline following marker.
				
				# 4: Content
				(
					(?>
						(?!\1 [ ]* \n)	# Not a closing marker.
						.*\n+
					)+
				)
				
				# Closing marker.
				\1 [ ]* (?= \n )
			}xm',
            array($this, '_doFencedCodeBlocks_callback'), $text);

        return $text;
    }
    protected function _doFencedCodeBlocks_callback($matches) {
        $classname = &$matches[2];
        $attrs     = &$matches[3];
        $codeblock = $matches[4];
        $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);
        $codeblock = preg_replace_callback('/^\n+/',
            array($this, '_doFencedCodeBlocks_newlines'), $codeblock);

        if ($classname != "") {
            if ($classname{0} == '.')
                $classname = substr($classname, 1);
            $attr_str = ' class="'.$this->code_class_prefix.$classname.'"';
        } else {
            $attr_str = $this->doExtraAttributes($this->code_attr_on_pre ? "pre" : "code", $attrs);
        }
        $pre_attr_str  = $this->code_attr_on_pre ? $attr_str : '';
        $code_attr_str = $this->code_attr_on_pre ? '' : $attr_str;
        $codeblock  = "<pre$pre_attr_str><code$code_attr_str>$codeblock</code></pre>";
        
        return "\n\n".$this->hashBlock($codeblock)."\n\n";
    }
    protected function _doFencedCodeBlocks_newlines($matches) {
        return str_repeat("<br$this->empty_element_suffix",
            strlen($matches[0]));
    }


    #
    # Redefining emphasis markers so that emphasis by underscore does not
    # work in the middle of a word.
    #
    protected $em_relist = array(
        ''  => '(?:(?<!\*)\*(?!\*)|(?<![a-zA-Z0-9_])_(?!_))(?![\.,:;]?\s)',
        '*' => '(?<![\s*])\*(?!\*)',
        '_' => '(?<![\s_])_(?![a-zA-Z0-9_])',
        );
    protected $strong_relist = array(
        ''   => '(?:(?<!\*)\*\*(?!\*)|(?<![a-zA-Z0-9_])__(?!_))(?![\.,:;]?\s)',
        '**' => '(?<![\s*])\*\*(?!\*)',
        '__' => '(?<![\s_])__(?![a-zA-Z0-9_])',
        );
    protected $em_strong_relist = array(
        ''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<![a-zA-Z0-9_])___(?!_))(?![\.,:;]?\s)',
        '***' => '(?<![\s*])\*\*\*(?!\*)',
        '___' => '(?<![\s_])___(?![a-zA-Z0-9_])',
        );


    protected function formParagraphs($text) {
    #
    #	Params:
    #		$text - string to process with html <p> tags
    #
        # Strip leading and trailing lines:
        $text = preg_replace('/\A\n+|\n+\z/', '', $text);
        
        $grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

        #
        # Wrap <p> tags and unhashify HTML blocks
        #
        foreach ($grafs as $key => $value) {
            $value = trim($this->runSpanGamut($value));
            
            # Check if this should be enclosed in a paragraph.
            # Clean tag hashes & block tag hashes are left alone.
            $is_p = !preg_match('/^B\x1A[0-9]+B|^C\x1A[0-9]+C$/', $value);
            
            if ($is_p) {
                $value = "<p>$value</p>";
            }
            $grafs[$key] = $value;
        }
        
        # Join grafs in one text, then unhash HTML tags. 
        $text = implode("\n\n", $grafs);
        
        # Finish by removing any tag hashes still present in $text.
        $text = $this->unhash($text);
        
        return $text;
    }
    
    
    ### Footnotes

    protected function stripFootnotes($text) {
    #
    # Strips link definitions from text, stores the URLs and titles in
    # hash references.
    #
        $less_than_tab = $this->tab_width - 1;

        # Link defs are in the form: [^id]: url "optional title"
        $text = preg_replace_callback('{
			^[ ]{0,'.$less_than_tab.'}\[\^(.+?)\][ ]?:	# note_id = $1
			  [ ]*
			  \n?					# maybe *one* newline
			(						# text = $2 (no blank lines allowed)
				(?:					
					.+				# actual text
				|
					\n				# newlines but 
					(?!\[.+?\][ ]?:\s)# negative lookahead for footnote or link definition marker.
					(?!\n+[ ]{0,3}\S)# ensure line is not blank and followed 
									# by non-indented content
				)*
			)		
			}xm',
            array($this, '_stripFootnotes_callback'),
            $text);

        return $text;
    }
    protected function _stripFootnotes_callback($matches) {
        $note_id = $this->fn_id_prefix . $matches[1];
        $this->footnotes[$note_id] = $this->outdent($matches[2]);

        return ''; # String that will replace the block
    }


    protected function doFootnotes($text) {
    #
    # Replace footnote references in $text [^id] with a special text-token 
    # which will be replaced by the actual footnote marker in appendFootnotes.
    #
        if (!$this->in_anchor) {
            $text = preg_replace('{\[\^(.+?)\]}', "F\x1Afn:\\1\x1A:", $text);
        }

        return $text;
    }

    
    protected function appendFootnotes($text) {
    #
    # Append footnote list to text.
    #
        $text = preg_replace_callback('{F\x1Afn:(.*?)\x1A:}',
            array($this, '_appendFootnotes_callback'), $text);
    
        if (!empty($this->footnotes_ordered)) {
            $text .= "\n\n";
            $text .= "<div class=\"footnotes\">\n";
            $text .= "<hr". $this->empty_element_suffix ."\n";
            $text .= "<ol>\n\n";

            $attr = "";
            if ($this->fn_backlink_class != "") {
                $class = $this->fn_backlink_class;
                $class = $this->encodeAttribute($class);
                $attr .= " class=\"$class\"";
            }
            if ($this->fn_backlink_title != "") {
                $title = $this->fn_backlink_title;
                $title = $this->encodeAttribute($title);
                $attr .= " title=\"$title\"";
            }
            $num = 0;
            
            while (!empty($this->footnotes_ordered)) {
                $footnote = reset($this->footnotes_ordered);
                $note_id = key($this->footnotes_ordered);
                unset($this->footnotes_ordered[$note_id]);
                $ref_count = $this->footnotes_ref_count[$note_id];
                unset($this->footnotes_ref_count[$note_id]);
                unset($this->footnotes[$note_id]);
                
                $footnote .= "\n"; # Need to append newline before parsing.
                $footnote = $this->runBlockGamut("$footnote\n");
                $footnote = preg_replace_callback('{F\x1Afn:(.*?)\x1A:}',
                    array($this, '_appendFootnotes_callback'), $footnote);
                
                $attr = str_replace("%%", ++$num, $attr);
                $note_id = $this->encodeAttribute($note_id);

                # Prepare backlink, multiple backlinks if multiple references
                $backlink = "<a href=\"#fnref:$note_id\"$attr>&#8617;</a>";
                for ($ref_num = 2; $ref_num <= $ref_count; ++$ref_num) {
                    $backlink .= " <a href=\"#fnref$ref_num:$note_id\"$attr>&#8617;</a>";
                }
                # Add backlink to last paragraph; create new paragraph if needed.
                if (preg_match('{</p>$}', $footnote)) {
                    $footnote = substr($footnote, 0, -4) . "&#160;$backlink</p>";
                } else {
                    $footnote .= "\n\n<p>$backlink</p>";
                }
                
                $text .= "<li id=\"fn:$note_id\">\n";
                $text .= $footnote . "\n";
                $text .= "</li>\n\n";
            }
            
            $text .= "</ol>\n";
            $text .= "</div>";
        }

        return $text;
    }
    protected function _appendFootnotes_callback($matches) {
        $node_id = $this->fn_id_prefix . $matches[1];
        
        # Create footnote marker only if it has a corresponding footnote *and*
        # the footnote hasn't been used by another marker.
        if (isset($this->footnotes[$node_id])) {
            $num = &$this->footnotes_numbers[$node_id];
            if (!isset($num)) {
                # Transfer footnote content to the ordered list and give it its
                # number
                $this->footnotes_ordered[$node_id] = $this->footnotes[$node_id];
                $this->footnotes_ref_count[$node_id] = 1;
                $num = $this->footnote_counter++;
                $ref_count_mark = '';
            } else {
                $ref_count_mark = $this->footnotes_ref_count[$node_id] += 1;
            }

            $attr = "";
            if ($this->fn_link_class != "") {
                $class = $this->fn_link_class;
                $class = $this->encodeAttribute($class);
                $attr .= " class=\"$class\"";
            }
            if ($this->fn_link_title != "") {
                $title = $this->fn_link_title;
                $title = $this->encodeAttribute($title);
                $attr .= " title=\"$title\"";
            }
            
            $attr = str_replace("%%", $num, $attr);
            $node_id = $this->encodeAttribute($node_id);
            
            return
                "<sup id=\"fnref$ref_count_mark:$node_id\">".
                "<a href=\"#fn:$node_id\"$attr>$num</a>".
                "</sup>";
        }
        
        return "[^".$matches[1]."]";
    }
        
    
    ### Abbreviations ###

    protected function stripAbbreviations($text) {
    #
    # Strips abbreviations from text, stores titles in hash references.
    #
        $less_than_tab = $this->tab_width - 1;

        # Link defs are in the form: [id]*: url "optional title"
        $text = preg_replace_callback('{
			^[ ]{0,'.$less_than_tab.'}\*\[(.+?)\][ ]?:	# abbr_id = $1
			(.*)					# text = $2 (no blank lines allowed)	
			}xm',
            array($this, '_stripAbbreviations_callback'),
            $text);

        return $text;
    }
    protected function _stripAbbreviations_callback($matches) {
        $abbr_word = $matches[1];
        $abbr_desc = $matches[2];
        if ($this->abbr_word_re)
            $this->abbr_word_re .= '|';
        $this->abbr_word_re .= preg_quote($abbr_word);
        $this->abbr_desciptions[$abbr_word] = trim($abbr_desc);

        return ''; # String that will replace the block
    }
    
    
    protected function doAbbreviations($text) {
    #
    # Find defined abbreviations in text and wrap them in <abbr> elements.
    #
        if ($this->abbr_word_re) {
            // cannot use the /x modifier because abbr_word_re may 
            // contain significant spaces:
            $text = preg_replace_callback('{'.
                '(?<![\w\x1A])'.
                '(?:'.$this->abbr_word_re.')'.
                '(?![\w\x1A])'.
                '}',
                array($this, '_doAbbreviations_callback'), $text);
        }

        return $text;
    }
    protected function _doAbbreviations_callback($matches) {
        $abbr = $matches[0];
        if (isset($this->abbr_desciptions[$abbr])) {
            $desc = $this->abbr_desciptions[$abbr];
            if (empty($desc)) {
                return $this->hashPart("<abbr>$abbr</abbr>");
            } else {
                $desc = $this->encodeAttribute($desc);

                return $this->hashPart("<abbr title=\"$desc\">$abbr</abbr>");
            }
        } else {
            return $matches[0];
        }
    }

}
